1. Field of the Invention
Present invention relates to a steel sheet to which resins are laminated in advance and which is used for a food can or the like and, more particularly, a laminated steel sheet suitable to welding.
2. Description of the Related Art
There are several methods of manufacturing cans: a soldered can making method, a welded can making method, a cemented can making method, a draw and ironing can making method, a draw and redrawing can making method, etc. The welded can making method uses simpler equipment at a lower cost than any other methods and can be carried out by easy and reliable operation. The cans made by this method have welded portions with high strength, so that they withstand severe working. For these reasons, the welded can making method has rapidly into wide use.
As the material for cans used in the soldered can making method and welded can making method, tinned steel sheets were initially used. Because a welded can has less coating weight than a soldered can, the wide use of the welded can making method is anticipated.
The sidewall and top end of food cans have been painted. The painting consists of thick-film painting for enhancing corrosion resistance of the inner surface of the can, painting for protecting the outer surface, printing, and the like. When the painting or the printing is performed, a steel sheet is cut to a predetermined size before being painted or printed. The process of the cutting and painting or printing requires a physical distribution cost as well as measures against environmental pollution due to painting. Therefore, the process has involved problems to be solved in can making.
So far, a laminated steel strip on which a film is laminated in a band form except for a welded portion has been proposed for welded cans. For instance, JP-A-H3-236954 (the term "JP-A-" referred to herein simplifies "unexamined Japanese Patent Publication") proposes a material for cans on which a thermoplastic film is laminated over a width corresponding to the height of a can except for a non-laminated portion 2 to 5 mm wide. The disclosed resins for the thermoplastic film are polyester, polypropylene, polyethylene, and nylon.
For the proposed material for cans mentioned above, however, consideration is not given to the fact that the adhesive force between the resin film and the base material is decreased by a thermal effect caused during a welding, touch-up painting of welded portion, or retorting. The resin film is blistered or separated by retorting.